Threshold plate



Nov. 3, 1942- R E. SPOKES THRESHOLD PLATE Filed Feb. 11, 1939 it 12a,

Patented Nov. 3;, 1942 UNITED res PATENT OFFICE THRESHOLD PLATE Application February .11, 1939, Serial No. 255,921 I 2 Claims.

This invention relates to threshold plates such as are used in refrigerator cars and like places, and to like articles which have heretofore been made of wood, metal and, in some instances, composition material.

The users of threshold plates and the like to which this invention pertains have laid down rather rigid specifications for such articles and this is particularly true in so far as articles made of composition material are concerned. Those articles which have been made of composition material heretofore and which complied with the aforesaid specifications have been made on an ordinary rubber binder formulation and have been, therefore, relatively expensive but at the same time not entirely satisfactory in use. Furthermore, appreciable, strength is a primary requisite of such articles.

In View of the foregoing and kindred problems an important object of the present invention is to produce relatively, inexpensive threshold plates of the aforesaid type'and like articles but which will nevertheless possess the requisite strength and other specified properties and an ancillary object is to employ materials which are less expensive than the materials which have been used heretofore in the manufacture of composition threshold plates and like articles.

It is often desirable that the articles to which this invention pertains possess good frictional properties and another object of this invention is to incorporate materials in the composition which will impart good frictional properties to the articles. It is, of course, desirable to employ materials for this purpose which will be inexpensive, since this invention primarily pertains to producing satisfactory articles at minimum cost, and therefore still another object is to employ waste materials that will impart good frictional properties to threshold plates and the like, a suitable source of such materials being finely ground brake material consisting of asbestos and other minerals and a cured binder such as is ground off the faces of friction elements in the course of manufacture thereof.

Inasmuch as appreciable strength is a primary requisite of articles such as those'to which this invention pertains a further object is to employ materials which will impart such characteristics to the articles and an object ancillary to this is to employ fibrous material such as asbestos for this purpose.

It is a still further object to'employ unvulcanized heavily frictioned fabric as an ingredient pertains and preferably to employ fabric of this type which is rich in rubber for so to do affords an economical source of bonding material and also this assists in affording articles possessing the desired appreciable strength.

This invention primarily consists in a novel composition for threshold plates or like articles, and in the hereinafter described novel method of making the same.

Other and further objects and features of the present invention will be apparent from the 'fol lowing description wherein reference is made to the accompanying drawing showing a typical embodiment of the invention and in which Fig. 1 is a perspective View of a threshold plate embodying the present invention; and

Fig, 2 is a transverse sectional view taken on the line 22 on Fig. 1.

The threshold plate illustrated in the drawing, and generally indicated by it), comprises an elongated rectangular body H of composition material. The body H has a rounded side-edge l2 which is adapted to be aligned with the outer edge of threshold of a refrigerator car or the like, and a tapered side edge I3. The body H also has holes hi therein for the reception of suitable fastening elements such as screws or the like. by which the threshold plate is secured in its position of use.

A preferred and suitable formula for the composition from which the new threshold plate is made is the following, in which all parts indicated are by weight: 7

Formula N o. 1

Parts Waste unvulcanized heavily frictioned fabric stock (such as trimmings from automotive vehicle tires in the course of manufacture thereof) (binder and reenforcement) 25 Reclaimed rubber (binder) 0.75 Parafiin wax (rubber'softener) 0.125 Sulphur (vulcanizing agent) 7.50 Mercaptobenzothiazole (rubber accelera- I tor) '0.30' Diphenylguanidine (rubber accelerator) 0.60 Inert filler, (preferably ground friction elementrmaterial comprised of asbestos, fillers and cured binder) 30.0 Asbestos (reenforcement) 55.0 Petroleum naphtha '-(solvent) 35.0 Lime 1.50"

The unvulcanized heavily frictioned fabric of articles such as those to which this invention stock referred to in Formula No. 1 consists largely serves to increase the rubber content and may be dispensed with entirely if the rubber content of the frictional fabric stock is sufficiently high.

However, no commercial supply of such stock with I a sufficiently high rubber content to permit the reclaimed rubber to be dispensed with has been 7 found. I

It should be noted, in this connection, that unused or new rubber might be used in place of the reclaimed rubber to increase the rubber content but to do so would materially increase the cost of the product. Likewise if new rubber was used in place of that derived from the frictioned fabric the cost of the composition would be so high as to prohibit its use.

The inert filler which is referred to in the foregoing example is waste material from the manuf-acture of automotive vehicle brake linings and like friction elements and principally from the operation of grinding the friction faces thereof. Such material imparts highly desirable friction properties to the products made from the composition.

While other fibrous material may be used in place of the specified asbestos I have found this material to be highly suitable.

Other petroleum or coal tar solvents may be used in place of the naphtha solvent which is specified in Formula No. 1.

It should also be noted that while the combination of rubber accelerators which is specified in Formula No. 1 produces very satisfactory results, including rapid acceleration, other rubber accelerators or mixtures thereof may be used, if desired, either alone or together with lime. However, a certain amount of lime, as indicated, is preferably employed since the lime expedites the cure of the rubber. An additional example of a suitable formula which may be followed in making the new composition is the following, in which all parts indicated are by weight:

Formula. No. 2

Parts Waste unvulcanized heavily frictioned fabric stock (such as trimmings from automotive vehicle tires in the course of manufacture thereof) (binder and reenforcement) Reclaimed rubber (binder) 0.75 Parafiin wax (rubber softener) 0.125 Sulphur (vulcanizing agent) 7.50 Mercaptobenzothiazole (rubber accelerator) 0.30 Diphenylguanidine (rubber accelerator) 0.60 Inert mineral filler (asbestine, blanc fixe or volcanic ash) 30.0 Asbestos (reenforcement) 55.0 Petroleum naphtha (solvent) 35.0 Lime 1.50

, It will be noted that Formula No. 2 is quite similar to Formula No. 1 and what has been which may be employed in the compositions to produce satisfactory threshold plates or like articles having the desired strength and resistance to breaking and bending forces and stresses.

However, the rubber content of the bond may be increased somewhat, if desired, as long as it ,is

-not increased sufiiciently to cause shrinkage in the product. Likewise, while the quantity of the frictioned fabric stock employed may be increased somewhat over the proportions or quantities specified, an excessive quantity of this material is to be avoided since such an excess results in the presence of too much cotton fiber in the products .with a resulting tendency to absorb excessive quantities of moisture and the like.

In the manufacture of threshold plates or like articles, the waste or scrap frictioned fabric stock is preferably first masticated although if available in relatively small particles it may be directly introduced into a rubber mill. In the course of manufacture the small particles of fabric stock, together with the reclaimed rubber, where used, and the parafiin, are worked together in a rubber mill. A suitable solvent, such as petroleum naphtha, is then added to form a cement. A suitable mixer is employed and the sulphur, lime, rubber accelerators, asbestos, and the other ingredients which are specified in the foregoing formulae are added, while mixing, to the aforesaid rubber cement, and the mixing is continued until all of the asbestos fibers are coated with the cement.

The mixture thus formed is then rolled into strips having a width, length and thiclmess somewhat greater than the desired dimensions of the desired finished products such as threshold plates, and these rolled strips are then subjected to a temperature of about 200- F. for a period of about forty-two hours for the purpose of removmg the solvent. The slabs thus formed are then pressed, while cold, until their thickness is somewhat less than that of the original strips, whereupon these pressed slabs are trimmed to the desired length. width and thickness.

Where the finished product is to be a threshold plate the side l3 of a trimmed slab is then tapered to an angle of about as shown, so that it will conform to the shape of the die into which the plate is to be placed. After such a plate is positioned in the die it is pressed in the die at a temperature of about 310 F. for a period of about seventy minutes, at a pressure of about one and one-half tons per square inch. Plates thus formed are thereafter cooled under pressure for a period of about fifteen minutes and are then finished to the desired thickness.

7 It will be seen from the foregoing formulae and description that the present invention accomplishes its objects, hereinbefore specified, and provides a new and improved threshold plate or like article and a new and. improved composition and method for making such threshold plates or like articles. Moreover such products, may be made in an eificient and relatively inexpensive manner.. ,This .is particularly true in view of the fact that the bond which is employed is composed largely of waste or scrap unvulcanized heavily frictioned fabric stock from automotive vehicle tire manufacture and the preferred inert filler which is employed is waste material from the manufacture of automotive vehicle brake linings.

While I have illustrated and described preferred compositions and a preferred method for carrying my invention into effect, these are capable of variation and modification, without departing from the spirit of the invention. I, therefore, do not wish to be limited to the precise details of the compositions and method set forth, but desire to avail myself of such variations and modifications as come within the scope of the appended claims.

I claim:

1. A new composition of matter especially adapted for use in making threshold plates and like articles and comprising a mixture of not substantially less than 25 parts of waste unvulcanized fabric material in the form of trimmings from automotive vehicle tires, as a binding and reenforcing agent, not substantially less than 0.75 part of reclaimed rubber, as a binder, not substantially less than 30.0 parts of inert filler, and not substantially less than 55.0 parts of asbestos, as a reenforcing agent, together with a rubber accelerator and a volatile solvent, all parts indicated being by weight.

2. A new composition of matter especially adapted for use in making threshold plates and like articles and comprising a mixture of not substantially less than 25 parts of waste unvulcanized fabric material in the form of trimmings from automotive vehicle tires, as a binding and reenforcing agent, not substantially less than 0.75 part of reclaimed rubber, as a binder, not substantially less than 30.0 parts of ground friction element material in the form of waste material from the manufacture of automotive vehicle brake dining or like friction elements and containing asbestos, fillers and cured binder, as inert filler, and not substantially less than 55.0 parts of asbestos as a reenforcing agent, together with a rubber accelerator and a volatile solvent, all parts indicated being by weight.

RAY E. SPOKES. 

